The present invention relates to a method for online measurement of a plasticizer in an endless filter rod of a filter rod maker. The invention relates also to a device for producing an endless filter rod in the tobacco processing industry.
EP 1 325 683 A2 discloses a method and a device for producing a fiber strand of the tobacco processing industry from a filter material having at least three components. The filter material is combined into an endless filter rod using an inlet funnel, and the proportions of the three components in the fiber strand are determined. For measuring the proportions, at least one portion is measured using electromagnetic waves in a first wavelength range, while a further portion is measured using electromagnetic waves in a second wavelength range. In addition, a microwave measurement system with a measuring head is provided that has a microwave source and a microwave detector. Two values are measured and evaluated at the microwave measurement system; this permits a statement to be made about the proportion of water and the common proportion in the strand of the chemically similar components, plasticizer and filter tow. The measurement method according to EP 0 791 823 A2 is used here. The measurement method can be used only where different material components can be detected by separate frequency ranges.
EP 1 895 291 A1 discloses a filter rod measuring station which is equipped with a measuring unit that measures at least the mass of a filter rod and the pressure drop of the filter rod, wherein a microwave measuring device is provided for measuring the mass of the plasticizer and/or the moisture content and/or the dry mass of the filter rod. These are at-line measurements, in which the sample to be measured is removed from the production process in order to deliver it for measuring the filter rod mass, the pressure drop of the filter rod and to the microwave measuring unit. Thus, only a minuscule part of the produced mass can be detected by the at-line operation.
U.S. Pat. No. 7,027,148 B2 discloses a method and a device for determining the triacetin content in a filter rod. The device has a filter tow container, a filter tow stretching and relaxation unit and a filter rod shaping unit. Here, the triacetin content in the filter rod is determined with a microwave resonator using the resonance frequency shift and the spread of the resonance line. To determine the triacetin content in this process, the linear relationship between the results acquired from the measurement variables is used, wherein for determining the offset values, the supply of triacetin is switched off periodically, and the endless filter rod produced without triacetin is measured as a reference value. Because these filter rods without triacetin must be treated as rejects, frequent taring often leads to unacceptable material consumption. Alternatively, a second microwave measurement unit along with speed sensors can be used for measuring reference values before the addition of triacetin; however, this drives up the cost for measuring triacetin sharply.
EP 1 480 532 B1 discloses a device for simultaneous, continuous measurement and regulation of the acetate and triacetin content in filter rods in the cigarette industry. Here, sensors are used for detecting the mass flow of filter tow material, and sensors are used for detecting the sum of the mass flow of filter tow material and plasticizer mass. With the production of the cigarette rods, sensors for measuring the mass flows are coupled in such a way that both the filter material mass and the plasticizer mass can be measured and regulated independently of each other. This measuring technique as a combination of two microwave units and a speed sensor also makes the measurement disproportionately expensive.
In the production of filter rods, generally several material parameters vary independently of each other:                a) The surface density of the filter tow material, that is, the filter tow mass per rod length. The surface density varies typically within short distances, and also occurs within a filter rod.        b) The titer of the filter tow varies with a change of the material used for the filter tow. The titer is typically specified as mass per fiber, and total mass per fiber band relative to a defined length. Due to defects during the production process, as a consequence of a filament breakage in the filter tow band, the total mass of the fiber band can change, so that the number of filaments per band can vary by approximately 2%. These variations can occur suddenly, but remain then over the distance of many filter rods.        c) The moisture of the filter tow material can vary. This variation often occurs slowly over the course of many filter rods, because to a certain extend moisture equalization occurs within the tow bale due to the long storage time.        d) The surface density of freshly applied plasticizer material can vary; triacetin is generally used here. The plasticizer, after hardening, provides the dimensional stability within the filter rod. The variation of the surface density of applied plasticizer material typically occurs over very short distances within a filter rod, and can have strongly fluctuating local concentrations.        e) In addition, during the production, the ratio in the endless filter rod of paper and glue can vary, and in particular the ratio of glue containing water and glue without water can vary. The variation of the ratios of paper and glue, or respectively within the glue, typically occurs relatively slowly within a larger distance over many filter rods.        
The previously disclosed online methods for measuring the content of plasticizer in an endless filter rod using a microwave resonator can only inaccurately detect the content of the plasticizer, due to the variation in content, or the methods are uneconomical due to the generation of rejects. Therefore, with all disclosed methods, additional measurement variables are used to reflect these variations, and thus permit a more accurate evaluation of the measurement variables of the microwave resonator. Often, this cannot occur online, as for instance with determining the pressure drop of the filter rod, or it requires further expensive measuring apparatuses at the filter rod maker.